The present invention relates to vertical shaft impact crushers, and more particularly to a vertical shaft impact crusher capable of autogenous, semi-autogenous, or impact crushing.
Impact crushers operate on the principal of accelerating the rock to a high speed and causing it to impact against a target which will cause the rock to fracture. There are essentially two types of impact crushers: autogenous impact crushers and anvil impact crushers. The autogenous variety uses a bed of the same material that is being broken or crushed as the target area so that the rock which is accelerated impacts against other rock of the same type. Anvil type impact crushers utilize a hard block of material such as manganese steel as the target area.
The autogenous and anvil types of impact crushers are used for different purposes. Autogenous crushing is used primarily for reshaping rock which is already approximately the right size. It is most frequently used on wash gravel or natural rock which is smooth and needs to be reshaped with flat faces so that it can be used as aggregate in concrete and the like. Autogenous crushing also produces a large number of fines, so that most of the product of autogenous breaking or crushing is at the two extreme ends of the product size spectrum. However, this crushing medium requires higher rotor tip velocities to achieve desirable reduction ratios. Higher rotor speeds increase horsepower requirements and substantially increase rotor wear.
Anvil breaking, on the other hand, produces a shattering action on the rock so that the majority of the product is near the central region of the product size distribution spectrum. Anvil breaking is used primarily to reduce the size of the input rock rather than to reshape rock which is already approximately the correct size. The anvil crushing ring thus generates higher reduction ratios at slower tip velocities, but does not generate a product shape of comparable quality to the autogenous apparatus, commonly known as the "rock box." The anvil ring reduces horsepower requirements and minimizes rotor wear by allowing for slower rotor speeds.
Impact rock crushers are often mounted on trailers for transportation from site to site, so that rock may be crushed at the location where it is needed. However, in the past, it has been necessary to use an autogenous crusher for autogenous crushing and to use an anvil crusher for anvil crushing. One solution to this problem is disclosed in commonly-assigned U.S. Pat. No. 4,560,113, where a vertical shaft impact crusher is provided with a pair of interchangeable breaker rings; one having anvils for impact crushing, and the other with a rock box for autogenous crushing. Thus, in this case the operator has a choice of performing either shaping or size reduction, but not a combination of both.
Thus, there has been a need for a vertical shaft impact crusher which is capable of adjusting or fine tuning the crushing process to more accurately control the size and shape of the crushed product.
It is therefore an object of the present invention to provide a vertical shaft impact crusher capable of autogenous, impact and/or semi-autogenous crushing simultaneously to produce a product of controlled shape and size.
It is a further object of the present invention to produce desired product at a desired volume at lower rotor velocities in order to reduce rotor tip wear and horsepower requirements.